26 Fungal Intro Flashcards
Define: Mykos: Mycology: Mycosis: Mycotoxicosis:
MYKOS: FUNGUS
MYCOLOGY: STUDY OF FUNGI
MYCOSIS: DISEASE CAUSED BY FUNGI
MYCOTOXICOSIS: DISEASE CAUSED BY A FUNGAL TOXIN
What is a fungus?
A eukaryotic, unicellular to filamentous, achlorophyllous organism having an absorptive nutrition. Reproduction can be sexual, asexual or both.
Why is the spectrum of antifungal drugs limited?
Beause humans and fungi are both eukaryotes and have many similar cell structures and metabolic pathways
Fungi are their own kingdom and have three Phyla. Compare the following in their diversity and defined sexual structures.
What are Ascomycota?
What are Basidiomycota?
What are Zygomycota?
A: largest and most diverse group of fungus. Sex reproduction structures have ASCI, which are sacs containging ASCOSPORES.
B: large and divers. Have BASIDUM where sexual spores are produced.
Z: named for the ZYGOSPORANGIUM where sexual spores develop.
What medically relevant pathogens are found in…
Ascomycota?
Basidiomycota?
Zygomycota?
A: Aspergillus and Candida (also Saccharomyces and Neurospora)
B: Cryptococcus neoformans
Z: Mucor sp
What is the main difference between fungal cell membrane and mammal cell membrane?
Fungus: ergosterol (except Pneumocystis)
Mammal: cholesterol
What is the main difference between fungal cell wall and plant cell wall?
Fungus: glucose and chitin with outer layer glycoproteins
Plant: cellulose
What is the difference between fungal cell wall and bacterial cell wall?
Fungus: glucose and chitin with outer layer glycoproteins
Bacteria: Peptidoglycan and muramic acid
T/F ALL medically important fungus have a cell wall.
TRUE
Are fugi motile?
No.
Fungal cell wall constitutes a large portion of its mass.
How does this affect replication time?
Slows replication.
What are the constituents of the cytoplasmic membrane, cell wall, and outer cell wall surface of fungi?
INNER
Cytoplasmic membrane – lipid bilayer with ERGOSTEROL and membrane proteins
Inner cell wall – GLUCAN AND CHITIN
Outer cell wall – GLYCOPROTEINS with fungal-specific cell wall anchorage
OUTER
What roles do carbohydrates serve on the cell wall? What are they made of?
1) Carbohydrates on outer surface of cell wall are attached to proteins.
2) Carbohydrates conferring rigidity to the cell wall are are polymers of glucose (glucan) and N-acetylglucosamine (chitin).
What makes up the inner layers of the fungal cell wall?
Inner layers: β (1,3) and β (1,6) glucan and chitin (60-70% cell wall mass)
What does the glucan polymers do for the cell wall?
What do the glucan and chitin polymers do for the cell wall?
β (1,3) and β (1,6) Glucan provide osmotic stability.
Glucan and chitin provide strength and rigidity
What makes up the outer wall layer of fungus?
Glycoproteins in outer wall layer: heavily modified with polysaccharides such as mannose (70% of glycoprotein mass is carbohydrate)
How is the outer cell wall of fungus built?
Why do we care? No really. Why?
maturation is typical of proteins secreted through the classical secretory pathway.
Both N- and O- carbohydrate linkages are used.
This pathway can be targeted in drug therapy.
What part of the cell wall activates innate immunity?
Humoral immunity?
1,3 glucan is a target for innate immunity
Glycoproteins protect and mask inner beta 1,3 glucan and elicit antibody production.
Glycoproteins function in adherence.
How many pathogenic fungi have capsules?
Name them.
One. Cryptococcus neoformans
How do fungi eat?
Fungi are absorptive heterotrophs. They absorb small molecules or breakdown complex organic molecules into smaller components that can be absorbed.
How do fungi compare to bacteria in terms of acid tolerance?
Fungi are more acid tolerant than bacteria in general.
Many grow optimally at pH 5.0 or below.
Useful for preparing media to favor growth of fungi when bacteria are present.
What is the name of an acidic agar medium used for fungal growth?
Sabouraud’s agar
What are secondary metabolites?
Synthesized by non-ribosomal peptide synthases (nRPS) and include both medically useful and toxic products.
What is an example of a toxic secondary metabolite (compounds not involved in normal growth) of fungi?
Aflatoxins that cause mycotoxicoses.
What two fungi often produce mycotoxicoses and are a concern in grain, bean, and nut production?
Aspergillus and Fusarium
What are two fungi that produce medically beneficial secondary metabolites?
Aspergillus terreus produces cholesterol lowering lovastatin
Fusarium heterosporum produces an anti-viral drug.
What are the two basic forms of fungal growth?
YEASTS (form smooth colonies)
HYPHAE (form molds)
What is a mycelium?
mass of hyphae
Slides 16 and 17 show the difference in growth via
Yeast Budding vs Hyphal Growth. What are some basics?
Budding is a form of splitting yeast cells
Hyphal is a thread-like filament tat may branch and may contain septa that divide the cytoplasm into segments. Each segment has a nucleus. Growth is polarized, ie one direction. It is said that some hyphae can grow through concrete
What is Aseptate aka Coenocytic?
Terms for a lack of hyphae
a multinucleate mass of protoplasm results from repted nuclear division unaccompanied by cell fission
What is Spitzenkorper?
a collection of vessicles near the tip that is specific to hyphal growth
What are Aerial vs Vegetative hyphae?
Aerial are reaching toward the air and can release spores.
Vegetative are submerged within the growth media and acquire nutrients
What is a Germ Tube?
The initial growth of a hyphae
What is a fungal spore?
a reproductive propagule that formes either sexually or asexually
What are Condidia?
asexual spores classified as micronidia (small, airborne, and often infectious) or macronidia (large and useful in identification)
What is Arthrospore?
a spore resulting from fragmentation of a hyphal filament
What are the advantages of hyphal growth?
Apical growth enables fungus to extend into fresh zones of substrate.
Tip extension can be rapid (40 micrometers/sec).
Hyphal tips have penetrating power.
Polymer degrading enzymes allow fungi to breakdown complex organic molecules.
What are pseudohyphae?
elongated yeasts which form under certain conditions
What is Thermal Dimorphism with regard to fungal growth?
Grow as yeast or as hypha depending on the temperature
What is Classical Thermal Dimorphism?
Fungus grow as hyphae in the environment, but as yeast once inside animal tissue.
What is the difference between Classical Thermal Dimophism and thermal dimorphism of Candida albicans?
In classical, only yeast form is found in animal tissue
With Candida, both hyphae and yeast form are found in animal tissue
What are two techniques of Lab Dx of fungus?
Direct observation (microscope) in situ (in animal tissue)
Culture
DNA probes
Serological tests
Explain the procedure for direct observation of fungus in animal tissue?
Use KOH or NaOH to dissolve the animal tissue
Fungus unaffected due to the cell wall
PAS periodic acid schiff or silver stain may be used
India ink may be used to observe capsule of Cryptococci neoformans (remember this is the only yeast with a capsule)
How do you observe Cryptococcus neoformans via microscope?
India Ink = neoformans capsule stain
Why are cultures of fungus sometimes dangerous?
Airborne spores
What is a distinguishing feature of pathogenic fungi?
Grow at physiological temperature
How do CD4 cells participate with immunity to fungi?
What can a weakened immune system do?
Th1 cells secrete interpheron gamma which stimulate macrophages»_space;
Leads to granulomatous formations
Weakened immune system can reactivate a latent fungal infection
What is the role fo Th17 cells in immunity to fungi?
Essential role against fungi in lungs and mouth
Th17 produce IL-17»_space; recruits neutrophils and activates epithelial cells on mucosal membranes to elicit antifungal defenses.
Pyogenic responses are elicited by some fungi
Individuals with low CD4 cells are susceptible to these types of infections:
fungal
T/F Fungal vaccines protect against infections.
There are no fungal vaccines
See Table 47-3 in Levinson! Notes tell you to memorize this. Flashcards soon.
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